The agents used as the antiulcer drugs include H.sub.2 -receptor antagonists, anticholinergic agents, gastric mucosal protective agents and antacids, which are used depending upon the symptom of patients. These known agents, however, are of such drawbacks as generally weak activity and frequent occurrence of side effects.
For example, cimetidine, which is a H.sub.2 -receptor antagonist widely employed, is known to have side effects such as gynecomatism. Moreover, numbers of cases are reported about recurrence of ulcer after suspension of administration with cimetidine. Anticholinergic agents are known to have such side effects as suppression of gastric motility, corediastasis and thirst. Furthermore, they exhibit activity only for a limited period of time. Antacids are known to have frequent occurrence of such side effects as constipation.
As described above, known antiulcer agents were limitedly used in terms of manner of administration due to their side effects, and they have common drawback of exhibiting somewhat weak activity.
Quinoxalinyl esters of carbamimidothioic acids are disclosed in Chem. Abstr. vol. 97, 216239k (1982), which are prepared by reacting 2-chloroquinoxalines with thioureas and useful as gastric secretion inhibitors and antihypertensives (no data).
The present invention results from efforts to develop new 4-thioquinazoline derivatives with more improved antiulcer effect.